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STAFF REPORT • • 5 MUSCO FAMILY OLIVE COMPANY AND THE STUDLEY COMPANY CONSIDERATION OF WDRS AND A C&A ORDER 6 September 2002 Regional Board Agenda is significantly lower than the anticipated stormwater runoff rate used to calculate the amount of stormwater runoff from land application areas. The discrepancy exists despite the soil moisture content at 100-percent. For example, in the month of March, stormwater runoff is anticipated to be approximately 26-percent of rainfall, while tailwater runoff is anticipated to be only 6-percent of the wastewater applied to land. The Discharger reports wastewater will be applied in short frequent applications to minimize stormwater runoff, but that approach requires the Discharger to operate the entire land application area with computer controlled spray equipment, which the Discharger has not yet fully installed. It is noted that the water balance predicts at least 5 inches of wastewater application in both March and April,but only 0.3 and 0.0 inches, respectively, of tailwater runoff is predicted. If the tailwater generation rate is higher than predicted, the wastewater storage pond will run out of capacity and in critical months, the lack of capacity will result in spilling of wastewater. The water balance's cumulative storage volume scenario is difficult to imagine. For example, at the end of February(with the storage pond containing 83.6 Mgal of wastewater), the storage pond will only accumulate 0.4 Mgal of additional wastewater despite the unfavorable conditions of rainfall exceeding evapotranspiration, 5.2 inches of applied wastewater, and 100-percent saturated soil. With all those factors to overcome, the water balance estimates 0.3 inches of tailwater runoff. Based on observations during site inspections, staff believes considerably more tailwater will be generated than what is described in the water balance. The water balance addresses the lack of capacity in the wastewater storage pond by establishing higher rates of leaching wastewater when the storage pond nears capacity. For example,the storage pond contains 83.6 Mgal at the end of February; in March the water balance then predicts 5.3 inches of leaching to prevent the pond from overfilling. If the leaching rate is less than expected, the pond will overfill and spill. Additional Restrictions Due to Water Balance Concerns One of the major problems with the water balance is that both tailwater and stormwater generation and storage rates are estimated. At this point, there is no way to verify the estimations except through direct measurements over the next few years. However, staff need to propose a flow limitation at this time. The tentative WDRs contain the Discharger's proposed flow limit of 800,000 gpd (as a monthly average), subject to a number of additional restrictions. The water balance indicated no wastewater would be applied during December, January, and February. This is consistent with the generally accepted practice of not applying wastewater in months when rainfall exceeds evapotranspiration rates. However the Discharger also wants to bypass stormwater around the wastewater storage pond during those months. Application of wastewater on the land application areas and then bypassing the wastewater/stormwater mix may result in discharge of wastewater off site, a situation which is expressly prohibited by the WDRs. Therefore, it is reasonable to include a prohibition against applying wastewater during the three